Bosch 520-HN-N User Instructions page 7

B An approved gas vent connector must be attached to
the top of the water heater and rise vertically at least
12" before entering into an approved gas vent
connector elbow.
B The minimum vertical gas vent height allowed is 6
feet; horizontal vent connectors and elbows are not
to be considered in the total gas vent height.
B All gas vent sections must be secured to each other
with sheet metal screws and be properly supported.
Horizontal runs:
Any gas vent section that is greater than 45 degrees
from the vertical is considered horizontal. Horizontal
sections must slope upwards at least ¼ inch for every
foot of its horizontal length and be properly supported.
Keep the horizontal section short and avoid too many
elbows. The maximum horizontal run allowed is half of
the total vertical vent height; horizontal vent connectors
and elbows are not to be considered in the total gas
vent height.
Vent termination:
The gas vent constructed of double wall Type B gas
vent must terminate above the roof surface with a listed
vent cap at a height that's in accordance with Fig. 7 and
table 2, provided they are at least 8 feet (2.4 m) from a
vertical wall or similar obstruction. All other gas vents
that are not able to terminate within the minimum
specified height allowed must terminate not less than 2
feet (0.6 m) above the highest point where it passes
through the roof and at least 2 feet (0.6 m) higher than
any vertical wall or similar obstruction within 10 feet (3.1
m).
LISTED VENT CAP
MINIMUM 6
FEET (1.8M)
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS
Fig. 5 Flat roof
6 720 644 942
LISTED GAS VENT
Fig. 6 Vent Adaptor for High Altitude Installations
Freeze prevention
In cold climates, components of a tankless water heater
can freeze and burst from negative draft. A leading
cause of negative draft is combustion appliances in the
building not being supplied with sufficient combustion
air. A wood stove or furnace can pull its combustion air
from the water heater's vent pipe, allowing the cold
incoming air to freeze the cold water in the heat
exchanger. Supplying more combustion air for all com-
bustion appliances is the solution. A HVAC specialist
should be consulted to design solutions for providing
more combustion air.
In cold climates where backdraft is a problem,
the freeze prevention kit accessory (7709003775)
should be installed.
Installation instructions
5" X 6" ADAPTOR
USED AT HIGH
ALTITUDE
7